/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.jena.sparql.engine.iterator;

import java.util.Map;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.function.Function;

import org.apache.jena.atlas.io.IndentedWriter ;
import org.apache.jena.sparql.core.Var ;
import org.apache.jena.sparql.engine.ExecutionContext ;
import org.apache.jena.sparql.engine.QueryIterator ;
import org.apache.jena.sparql.engine.binding.Binding;
import org.apache.jena.sparql.serializer.SerializationContext ;

/**
 * This class provides the machinery for trackable iterators.
 */
public abstract class QueryIter extends QueryIteratorBase
{
    // Volatile just to make it safe to concurrent updates
    // It does not matter too much if it is wrong - it's used as a label.
    private volatile static int iteratorCounter = 0 ;
    private int iteratorNumber = (iteratorCounter++) ;

    private ExecutionContext tracker ;

    public QueryIter(ExecutionContext execCxt) {
        super(cancelSignal(execCxt));
        tracker = execCxt ;
        register() ;
    }

    private static AtomicBoolean cancelSignal(ExecutionContext execCxt) {
        if ( execCxt == null )
            return null;
        return execCxt.getCancelSignal();
    }

    public static QueryIter makeTracked(QueryIterator qIter, ExecutionContext execCxt) {
        if ( qIter instanceof QueryIter )
            return (QueryIter)qIter;
        return new QueryIterTracked(qIter, execCxt);
    }

    public static QueryIter materialize(QueryIterator qIter, ExecutionContext execCxt) {
        return makeTracked(materialize(qIter), execCxt);
    }

    public static QueryIterator materialize(QueryIterator qIter) {
        return new QueryIteratorCopy(qIter);
    }

    public static QueryIterator map(QueryIterator qIter, Map<Var, Var> varMapping) {
        return new QueryIteratorMapped(qIter, varMapping);
    }

    /** flatmap.
     * The mapper may return null to signal "no iterator for this binding"
     */
    public static QueryIter flatMap(QueryIterator input, Function<Binding, QueryIterator> mapper, ExecutionContext execCxt) {
        return new QueryIterRepeatApply(input, execCxt) {
            @Override protected QueryIterator nextStage(Binding binding) { return mapper.apply(binding); }
        };
    }

    @Override
    public final void close() {
        super.close();
        deregister();
    }

    public ExecutionContext getExecContext() {
        return tracker;
    }

    public int getIteratorNumber() {
        return iteratorNumber;
    }

    @Override
    public void output(IndentedWriter out) {
        output(out, null);
        // out.print(Plan.startMarker) ;
        // out.print(Utils.className(this)) ;
        // out.print(Plan.finishMarker) ;
    }

    @Override
    public void output(IndentedWriter out, SerializationContext sCxt) {
        out.println(getIteratorNumber());
    }

    private void register() {
        if ( tracker != null )
            tracker.openIterator(this);
    }

    private void deregister() {
        if ( tracker != null )
            tracker.closedIterator(this);
    }
}
